Much of the millions of metric tons of plastic waste that washes into
the sea each year is broken down into tiny fragments by the forces of
the ocean, and researchers are beginning to piece together what this
means for organisms that consume them. Scientists in Korea have turned
their attention toward the top of the food chain by exploring the threat
these particles pose to mammal brains, where they were found to act as
toxic substances.
To further our understanding of these dangers, researchers at Daegu
Gyeongbuk Institute of Science and Technology orally administered
polystyrene microplastics two micrometers in size or smaller to mice
over the course of seven days. Like humans, mice have a blood-brain
barrier that prevents most foreign substances, and especially solids,
from entering the organ, but the scientists found that the microplastics
were able to make their way through.
Once in the brain, the scientists found that the particles built up in
the microglial cells, which are key to healthy maintenance of the
central nervous system, and this had a significant impact on their
ability to proliferate. This was because the microglial cells saw the
plastic particles as threat, causing changes in their morphology and
ultimately leading to apoptosis, or programmed cell death.
Additionally, the scientists carried out experiments on human
microglial cells and also observed changes in their morphology, along
with changes to the immune system via alterations to the expression of
relevant genes, related antibodies and microRNAs. As seen in the mouse
brains, this also induced signs of apoptosis.
“The study shows
that microplastics, especially microplastics with the size of 2
micrometers or less, start to be deposited in the brain even after
short-term ingestion within seven days, resulting in apoptosis, and
alterations in immune responses, and inflammatory responses," says study
author Dr. Seong-Kyoon Choi." Based on the findings of this research,
we plan to conduct additional research that can further reveal the brain
accumulation of microplastics and the mechanism of neurotoxicity."